The present invention relates to a balance with a weighing compartment that borders on a stationary part of the balance and is otherwise enclosed by at least one side wall, a front wall, and a top cover panel, where at least one of the walls and/or the top cover panel is slidable by means of a guiding device to open and close the weighing compartment.
A known balance of this kind, as described for example in the European patent application EP-A-0 234 008, has a weighing pan and a weighing compartment that encloses the weighing pan on all sides, with a stationary front glass wall, rearward-sliding side walls, a rearward-sliding top cover panel, and a connector that joins the side walls with the top cover panel. The connector is configured so that when a side wall and/or the top cover panel is opened or closed, the connector moves together with the side wall and/or the top cover panel, so that the weighing compartment is freely accessible without being obstructed by frame members on the sides. Furthermore, the side walls can be opened and closed individually or together, with or without moving the top cover panel at the same time. The movement can be motorized or manual. With manual operation, the walls that are to be moved are uncoupled from the motorized drive mechanism.
The European patent application EP-A-0 574 668 discloses a balance that has a draft-protection housing with a top cover panel that can be attached or taken off by means of a manually operated locking arrangement. After the top cover panel has been taken off, the front wall as well as the side walls can be completely removed from the housing for cleaning. In this known design of a balance, the top cover panel is part of a frame that holds the draft-protection housing together. To a certain extent, the walls are unobstructed by the frame members so that the operator has a better view of the interior of the housing, but for some applications, this design is still not entirely satisfactory. One drawback is that the upper part of the frame is still a required element, and another concern is that the locking elements, which have to be manufactured with high precision, require a certain amount of manipulation in order to align them with the recesses in which they are received.
In state-of-the-art balances, if conduits, hoses, or other connections have to be introduced into the weighing compartment in a flexible, non-permanent arrangement, a slidable side wall or the top cover panel has to stay at least partially open during the weighing process, because the rigid frames and complicated guiding devices do not allow the walls to be provided with individual, easily accessible conduit passages. However, leaving a wall open can cause errors in the weighing result.
In essence, known balances suffer from the drawback that they don""t simultaneously allow free, unrestricted access to the weighing compartment as well as an unobstructed view of the weighing pan. Simultaneous access from the side and from above is not possible, a problem that applies in particular to the accessibility for conduits, hoses or other connections. In addition, the weighing compartment is difficult to clean.
It is therefore the object of the present invention, to provide a balance with a weighing compartment that simultaneously offers an unobstructed view of the weighing pan and good accessibility in all situations, and to accomplish this objective through a simple concept that also makes the manipulation easy for the user. The weighing compartment should be conveniently accessible for placing a sample on the pan when the walls are open, and it should allow the passage of conduits and cables with the wall completely closed. In addition, it should be easy to clean, without the need for complex manipulations.
The present invention offers a solution to the aforedescribed problem in a balance with a weighing compartment that borders in part on a stationary part of the balance and is otherwise enclosed by at least one side wall panel, a front wall panel, and a top cover panel panel, where at least one of the walls and/or the top cover panel is slidable by means of a guiding device to open and close the weighing compartment. According to the invention, a holder arrangement for the at least one slidable wall panel is integrated in the guiding device, and a holder arrangement for each of the non-slidable wall panels is integrated in the stationary part of the balance. Each wall panel is releasably held in position by its respective holder, which can be locked and unlocked by engaging and disengaging a form-locking closure device that is operated simply by applying a force to the wall panel and/or the holder arrangement.
The side walls, the front wall, and the top cover panel can be individually separated by hand from the balance by simply pulling at them lightly to tilt them outwards, e.g., for easy cleaning of the wall plates, which are normally made of glass. When they are in their working position, the walls are positively locked into place. The same hand movement is used to unlock each of the walls. Besides making the weighing compartment easy to disassemble for cleaning, the concept of integrating the holder arrangements of the slidable walls in the guiding devices also accomplishes the objective of making the weighing compartment freely accessible and of allowing an unobstructed view of the weighing pan even when the weighing compartment is closed, with no sight-blocking frame members being in the way.
It is advantageous if at least one of the holder arrangements contains a snap-closure body for an automatic snap connection of the respective wall panel. Preferably, the snap-closure body is attached to the rear wall of the weighing compartment and designed as a holder and guide for the side walls.
The concept of at least one snap-closure body to hold, e.g., the side walls in their operating position is particularly favorable for a design without frame members. The kind of support frame that is required with prior-art designs is not necessary in balances according to the present invention. A snap-closure body can be manually operable, so that a wall can be attached or released by, respectively, pushing or pulling at the wall. A snap-closure body is designed so that a larger amount of force is required to pull off a wall panel than to snap it into place, so that the wall panel is held in place very securely. The special shape of the snap-closure bodies and their design as a single-piece plastic article make them particularly cost-effective to produce.
To keep out air drafts that could enter at the joints between the walls of the weighing compartment, a further embodiment of the inventive balance has edge joints where the edge of one wall is seated in a groove of the other, or one wall has an edge-cover strip to close off a gap that could form at the joint between the two walls.
A preferred embodiment of the balance has a means for driving the movement of the at least one slidable wall panel. Preferably, the drive means are designed as cord-pulley drives.
The slidable walls are releasably attached to guiding devices with couplers or clutches by which the guiding device for each individual wall panel can be connected to or disconnected from the drive means. The couplers are provided with levers so that they can be operated by hand. As a result, the side wall panels and/or the top-cover panel can be driven either individually or together or in any desired sub-combination. For example, it is possible to open and close only one side wall, or only the top cover panel. Advantageously, the coupler arrangement includes traveling coupler elements that automatically seek and find the position for engagement. For example, if a side wall is uncoupled from the drive, pushing the coupler actuator on the side wall will cause the latter to be coupled to the drive as soon as the traveling coupler element of that side wall has reached its counterpart on the wall panel.
In an advantageous embodiment of the invention, the drive means are powered by only one motor.
According to a further embodiment of the invention, the travel distance between the open and closed positions can be different for the side walls than for the top cover panel, in which case the movements of the respective drive means can be synchronized by using different transmission ratios corresponding to the different travel distances. Thus, the same motor can be used to drive the side walls and the top-cover panel.
The balance is preferably equipped with a carrying handle. Thus, the balance can, e.g., be lifted from the table with one hand, while cleaning the table surface underneath the balance with the other hand. As a special feature of the invention, the carrying handle serves at the same time as a guide rail for the guide element of the top-cover panel, with a guiding device being arranged on the handle. In an advantageous embodiment, the guiding device has at least one gear rack in an upper area of the guiding device and a parallel gear rack in a lower area. A vertical body of the guide element contains a pair of identical gears fixed on a vertical axle and rolling along the gear racks, whereby the guide element is held in alignment and prevented from jamming as it moves back and forth. This vertical arrangement of the guide element has the advantage that it minimizes the length of the guiding device for the top cover panel.
In a particularly preferred embodiment of the balance according to the invention, passage openings are provided in the side walls, the front wall, the top cover panel, and/or the rear wall of the weighing compartment for conduits and cables. The passage openings can be closed off against air drafts by means of clip-on covers. This concept has a multitude of possible applications where experiments are conducted inside the weighing compartment and weight changes are observed as part of the experiment, for example when reagents are dispensed into a beaker on the balance pan, or when a chemical reaction is being studied. A design without frame members along the edges and the possibility of tilting the walls outwards without removing them from the balance provides a simple way of running electrical supply and signal cables or conduits for fluids and gases through the cutout passages, to secure the cables and conduits in the cutout openings, and to seal the latter against air drafts by means of special clip-on holders. Special configurations of the clip-on devices, e.g., as holder elements, expand the range of their possible uses.
A special embodiment of the balance according to the invention has an accessory unit arranged, e.g., at the rear of the balance. The accessory unit contains power supplies and/or control units. Cables connected to this accessory unit through openings can be routed to the cutout passages through special guide channels along the housing, so that they will not interfere with the movement of the side walls.